Throughout this application various publications are referred to as references, within parentheses or by footnote. The procedures set forth in these publications where relevant are hereby incorporated by reference. The reasoning set therein is also incorporated by reference in so far as it does not differ from or conflict with the text herein. In case of such difference or conflict the text herein controls.
Cells contain vesicles (also called endosomes) that are spherical structures with a bilipid membrane. These endosomes can merge with the cell membrane and release their content into the extracellular environment (exocytosis). The process of forming vesicles and merging them with cellular membranes can be broadly divided into two categories: constitutive and regulated. Constitutive exocytoses are maintenance functions of the cell while regulated exocytoses is a specialized response of the cell to an external or internal signal. The paradigm of specialized regulated secretion is the release of neurotransmitters at neuronal synapses. At the proper signal (usually a drop in cell voltage) hundreds of vesicles merge with the cell membrane to release their neurotransmitters. The neurotransmitters diffuse across the synaptic space to bind to and excite the postsynaptic membrane of a second neuron.
Exocytosis requires specialized proteins on the vesicle and presynaptic membrane that are collectively known as the SNARE proteins. Removal of any of these proteins can stop vesicle docking to membrane and block or decrease neural signaling. One protein on the vesicle membrane called VAMP (vesicle associated membrane protein) and one on the presynaptic membrane called SNAP (synapse associated protein) are the targets of the botulinum and tetanus neurotoxins from the Clostridial bacterium.
Botulinum toxin (BT) is a potent neurotoxin produced by the anaerobic gram-positive bacterium Clostridia botulinum and the closely related species Clostridia butyricum and beratti. When spores of the Clostridia botulinum are ingested they germinate and secrete BT that passes from the GI tract into the systemic circulation. The systemic spread of BT causes the disease botulism that is characterized by widespread neuromuscular paralysis.
BT is a protein consisting of a light and heavy chain that together weigh approximately 150 kilodaltons. BT works by a three-stage mechanism, binding, translocation into the neuron and molecular action, each of which is performed by separate 50 kilodalton domains. The binding and translocation domains make up the heavy chain, while the catalytic action is performed by the single domain of the light chain.
At present seven immunologically distinct serotypes of the BT are known, named A, B, C, D, E, F and G. The effect of BT is to inhibit the release of neurotransmitters and neuropeptides by neurons. Although all BT serotypes interfere with proteins that cause the exocytosis of synaptic vesicles from cells they each interfere with different proteins, or different parts of the same protein. In clinical use each serotype appears to differ in its potency in blocking different classes of neurons.
BT binds to specific molecules present on neuron presynaptic membrane. After binding it is internalized into the neuron by formation of an endosome. When the interior of the endosome becomes acidic, the light chain translocates across the membrane and is released into the cytoplasm. After translocation across the cell membrane the CT light chains cleave the proteins involved in synaptic vesicle docking and release that are collectively known as SNARE proteins. The targets of the CT are the following:
BT A & E cleave SNAP-25 (synapse associated protein)
BT C cleave SNAP-25 and syntaxin
BT B, D, F & G cleave VAMP (vesicle associated membrane protein)
The vesicles within neurons contain classical neurotransmitters (acetylcholine, epinephrine, norepinephrine, dopamine, serotonin, glutamate, GABA and others) and/or neuropeptides (substance P, neurokinin A, calcitonin gene related peptide (CGRP), neuropeptide Y, interleukins, growth factors and others). BT has been shown to block secretion of all these molecules.
The Clinical Effects of Botulinum Neurotoxin
Voluntary Motor Nerves
The first and still primary use of BT is to block motor nerve communication with muscle fibers. BT is injected within the target muscle. The BT is then internalized into motor neurons where it decreases or stops the release of the neurotransmitter acetylcholine (AChE), thereby causing paresis or paralysis of the muscle. Scott introduced the concept of localized muscular injections of BT for the specific condition of strabismus (squint, crossed eyes). Later BT was found to be particularly useful for movement disorders such as tics, spasms, contractures, cramps and tremors. More recently, the injection of BT into facial muscles has been found to ameliorate skin wrinkling and lines related to aging. Another recent application of BT injections is to decrease the pain accompanying muscle tension in conditions such as headache and temporomandibular joint syndrome.
Autonomic Motor Neurons
The autonomic nervous system is divided into a parasympathetic system and a sympathetic system. The parasympathetic neurons use acetylcholine as their neurotransmitter and they can be blocked with BT. The sympathetic nervous system uses noradrenaline as its neurotransmitter with the single exception of sweating) and this neurotransmitter is not blocked by BT. Effector neurons of the parasympathetic system innervate and control the contraction of smooth muscles. Injections of BT have been used to decrease tone in the smooth muscles of the lower esophageal sphincter, esophagus, stomach wall, and pyloric sphincter, sphincter of Odi, anal sphincter, and urinary bladder.
Autonomic Secretory Neurons
In addition to their innervation of smooth muscle, neurons of the autonomic system control or modulate a wide variety of other functions such as the secretion of various glands throughout the body. BT injections have been used to decrease gastric secretions including acid production, nasal and other respiratory secretions, and tearing.
Neuropeptides
In addition to the neurotransmitters released at localized synaptic sites, many autonomic and sensory nerves can release neuropeptides along part or all of the length of the axons. These peptides are most noticeable in skin as mediators of inflammation, allergic reactions and pain. For example injury in a small area of skin causes reflex vasodilation in surrounding areas. These reactions are neurally mediated and depend on the release of neuropeptides. Although the neurogenic vasodilation of skin is blocked by BT, whether other phenomenon such as pain and swelling are blocked is still controversial.
Tetanus Toxin
Tetanus toxin (TT) is produced by the Clostridium tetani bacterium. When Clostridium tetani spores infect wounds they germinate and produce TT. The TT is taken up by peripheral nerves near the wound and transported retrograde to the central nervous system. It then spreads by diffusion and further neural transport. At low doses TT blocks release of the inhibitory neurotransmitters GABA and glycine causing increased activity in motor and autonomic nerves. Clinically the condition is called tetanus and is characterized by severe muscular spasms and autonomic instability. However, at higher doses TT blocks all neurotransmission and clinically this appears as a flaccid paralysis.
TT also works by a two-stage mechanism that is similar to BT. However; the major difference is that after the peripheral neuron internalizes the TT via endosomes the TT is not released into cytoplasm. Instead the endosomes are actively transported back to the cell body of the neuron. Here TT is again released into all synapses. At low doses the blocking is selective for inhibitory neurons. However, at higher doses TT blocks all neurons both inhibitory and excitatory, centrally and peripherally.
TT also differs from BT in that it is taken up by more classes of neurons and at lower doses then BT. As described above the effect of excitation or inhibition of a given neuron by TT are dose related. Peripheral block of a neuron requires 10-1000 times the dose that causes excitation of that same neuron. However, hybrid molecules of TT, such as those that combine the heavy chain of BT with the light chain of TT, could be expected to have the same dose effects of as whole BT.
Skin Secretory Glands
Secretion is the combined result of production of secretion by specialized cells within a skin gland, and the expulsion of the secretion from the gland and ducts by contraction of surrounding muscle-like myoepithelial cells. In some secretory glands, such as the mammary gland, increased expulsion has a feed back effect in stimulating further secretory production. In addition, the number and amount of secretory and myoepithelial cells can be modulated, with proportional changes in the amount of secretion produced. Finally the act of secretion is often accompanied by vascular dilation around the gland, which is believed to aid the gland by increased delivery of nutrients.
Skin secretory cells produce their secretion by 3 basic mechanisms.
Apocrine glands are the common sweat glands present throughout the skin surface that produce profuse watery secretion. Apocrine glands have a simple organization; the gland is composed of a coiled duct in the derm is with an open end that discharges onto the skin surface. They produce a watery secretion that evaporates and cools the skin thereby playing a role in thermoregulation. Discharge of the secretion from the lumen of the ductal portion of the apocrine sweat gland is assisted by the action of myoepithelial cells which surround the secretory portion of the gland.
The cells lining the ducts of apocrine glands produce the secretion by a merocrine mechanism. This terminology is confusing as it would appear that this sweat glands should be called merocrine glands. However, the sweat glands were named before the exact mechanism of their cellular secretion was known, and their original names have persisted.
Excessive sweating, formally known as hyperhydrosis, is a common condition. Hyperhydrosis can occur in any part of the body but primarily affects the forehead, axilla, palms and feet. Sanders and Shaari (U.S. Pat. No. 5,766,605) Walker (U.S. 20020086036) disclose a method of treating hyperhydrosis using needle and jet injections of BT.
Eccrine glands are commonly thought of as specialized sweat cells that produce a secretion with high protein content. Eccrine sweat glands are found in the axilla, in the areolae of the breast and around the anus. They are larger than apocrine sweat glands and produce a viscous secretion into hair follicles. The secretion released by apocrine sweat glands is odorless but the bacteria metabolize the secretion and decompose its proteins, thereby causing a strong odor, which is usually experienced as unpleasant.
WO03026602A2: Medicine For Preventing And Treating Bromidrosis discloses the use of BT injections of BT for decreasing the odor of sweat.
Holocrine glands are fundamentally different from apocrine and eccrine glands. The secretion is primarily lipid rather than water. Moreover the lipid secretion is not secreted from cells; instead the cell, called acebocyte, accumulates large amounts of the secretion and then dies, releasing the lipid material together with cellular remnants.
The vast majority of holocrine glands are sebaceous glands that produce a lipid secretion called sebum. Sebaceous glands usually have several acini that open into a short duct. The sebum producing cells are present in the acini and in the wall of the duct. Most sebaceous glands are called pilosebaceous glands because they secrete into a duct that normally opens into the upper part of a hair follicle. However, in certain areas of the body such as the lips the ducts open directly onto the skin's surface. A variety of other holocrine organs are present in the skin of the eyelids: meibomium glands, and glands of Zeiss and Moll.
The control of holocrine glands has long been known to involve systemic hormones, particularly the male sex hormones called androgens. Androgens increase during puberty in both males and females. Supporting the connection between hormones and sebaceous gland function is that sebum production increases after puberty and its peak incidence is from ages 12 to 22. Increased sebum production is also related to pregnancy, pre-menstrual period and to birth control medication.
The role of classical neurotransmitters such in sebum production is unclear. Anticholinergics appear to have little effect on sebum production. However, pilocarpine, a cholinergic agonist, increases sebum production when iontophoresed across the skin (Yosipovitch et al, Br J Dermatology, 1995: 561-4). Evidence suggests that increased sebum production in response to cholinergics may be due more to expulsion of accumulated sebum rather then increased cellular secretion. Even facial movement seems to be important in emptying accumulations of sebum as patients with facial paralysis accumulate greater amounts of sebum.
Dopamine appears to play an inhibitory role in sebum secretion as patients with Parkinson's disease, a disease in which central nervous system levels of dopamine are low, have been reported to have increased sebum production. Treatment of these patients with dopaminergic drug therapy appears to decrease sebum levels whereas anticholinergic drugs have no effect (Villares, Arq Neuropsiquiatr, 1989, 47: 31-8). However, the dopaminergic effects on sebum production may be within the central nervous system, or to increase facial movement as untreated Parkinson's patients have decreased facial movement.
Recent research has shown that surprisingly, holocrine secretion is controlled by various neuropeptides, with substance P playing a significant role (Toyoda and Marohashi, Med Electron Microsc 2001, 29-40). Other neuropeptides found in neurons surrounding sebaceous glands include NPY, VIP and ENK, although their roles are unclear.
Mixed glands are skin secretory glands in which holocrine components are mixed with apocrine or eccrine components. Holocrine components have been reported in the cerumen glands that produce ear wax (Main and Lim, Laryngoscope, 1976, 86:1164-76) and mammary glands that produce milk.
Clinical Conditions Affecting Holocrine Glands
Acne Vulgaris
One of the most common disorders of the sebaceous glands is Acne Vulgaris (acne). Acne is largely a disease of adolescence and young adulthood characterized by inflamed glands within the skin of the face, shoulders, and back. It is estimated that almost all people suffer at least some acne during their lives.
Excessive sebum production within pilosebaceous glands results in an enlarged and obstructed sebum gland. These obstructed glands are highly susceptible to infection by Propionibacterium acnes (P. acnes) causing an inflamed pustule called a comedone. These inflamed pilosebaceous glands can cause permanent scaring of skin.
Current therapy of acne includes topical and oral agents. Topical retinoic acid is the treatment of choice for non-inflammatory acne. Benzoyl peroxide and/or topical antibiotics are used to treat inflammatory acne including papules pustules and cysts. Systemic antibiotics are also used for inflammatory acne.
Systemic therapy consists mainly of systemic antibiotics, usually tetracycline, to decrease bacteria until the patient is in remission; then a lower dose is used for maintenance. Oral isoretinoin inhibits sebaceous gland function and keratinization by an unknown mechanism. However due to its severe side effects, including liver disease and birth defects, its 16-20 week course is reserved for severe acne unresponsive to conventional therapy.
Seborrheic Dermatitis (Seborrhea)
Seborrhea is an acute or subacute skin disorder of unknown etiology presenting as eruptions in skin areas containing many sebaceous glands. The scalp and face are most common and may result in hair loss (alopecia). Lesions are red to yellow and may be itchy and scaly. Treatment includes removal of scales with frequent washing and shampooing with selenium sulfide suspension, zinc pyrithione, or tar and salicylate shampoo.
Sebaceous Cyst
Obstruction of a single sebaceous gland may result in an intra dermal cyst. These can occur anywhere on the body and become infected and form abscesses. Treatment includes oral antibiotics, surgical drainage and/or excision of the cyst.
Seborrheic Blepharitis (Blepharitis)
The holocrine glands of the eyelid are called mebomium glands. They produce an oily substance that aids in lubricating the exposed surface of the eye. Blepharitis is an acute to chronic condition that presents as a burning and itching of the eyelids. Signs are waxy scales on the eyelashes, loss of eyelashes, and lid ulceration and secondary infection with Staphylococcus aureus.
Treatment includes meticulous hygiene, mild shampoo, and topical antibiotics.
Rosacea and Rhinophyma
Although the cause of rosacea is unknown, it is closely associated with and involves sebaceous glands. Rosacea is a chronic condition that begins as periodic facial flushing and progresses to telangestasia, papules, pustules and nodules. It is more severe in men and often associated with rhinophyma, thickened bulbous skin of the nose. Treatment of acne like rosacea includes topical or systemic antibiotics, topical steroids and Sulfacet-R lotion.
Furuncles, Carbuncles, Pustules, Chalazions, and Styes
Skin infections often begin in pilosebaceous glands. In acne the infectious bacterium is P. acnes. However many conditions begin with an inflamed pilosebaceous gland and are secondarily infected with other bacteria such as Staphylococcus aureus and Streptococcus epidermis. Single small infections are called furuncles, larger ones are called pustules and when subdermally spread to create large fluctuant abscesses called carbuncles. In the eye, analogous infections of the specialized holocrine glands are called styes and chalazions. Treatment of these conditions includes warm compresses, topical and systemic antibiotics, and often surgical drainage.
Excessive Sebum
More of a cosmetic condition then a medical one, excessive sebum production is quite common. Most often the central area of the face is affected, and this area looks and feels greasy. Treatment is frequent washing of the face with strong soaps. This often causes secondary drying of the remaining areas of the skin.
Excessive Cerumen
Cerumen is produced by mixed holocrine like glands in the skin of the ear canal and its production is at least partly under cholinergic control. Cerumen normally slowly migrates outward and is lost from the meatus of the ear canal. In some patients cerumen accumulates within the ear canal, sometimes to the point of impaction. This can cause underlying infection of the ear canal called otitis externa and decreased hearing due to poor sound transmission. Treatment includes cerumen dissolving chemicals such as carbamide peroxide and/or manual removal of the wax by a physician.
Mammary Secretion
During and after pregnancy the mammary gland produces breast milk. Although lactation is principally hormonal the secretion and expulsion is influenced by neurotransmitters. Cattle with low grade botulinum toxin poisoning have been noted to have dramatically decreased milk production despite normal appetites.
Lactation is natural and necessary for breast feeding the newborn. However not all mothers wish to breast feed, and in cases of miscarriage or stillborn the presence of breast fluids is a painful psychological reminder of the loss. Finally the increase in size of the breast during the pregnancy and post partum period eventually involutes, contributing to a cosmetic undesirable loss of tone in breast tissue.
U.S. 20020094339A1: Methods For Treating Mammary Gland Disorders discloses the use of CT to decrease the size of mammary glands and secondarily decrease the incidence of mammary malignancies.
At present there is a large need in the art for compositions and methods of inhibiting secretions of holocrine glands.